Overview
At Ullanor, the Emperor’s armies broke a great ork empire and assembled to celebrate the victory. Horus was raised to Warmaster before the Legions. The ceremony belonged to an Imperium still able to regard its greatest surviving armies as forces on the same side.
Ullanor Prime later became Armageddon. After the War of the Beast, the Mechanicus moved the stripped world using captured ork teleportation technology, concealed what they had done and left it to be colonised under another name. This marker records the historical position. The people living on the relocated planet inherited its ground without being given an honest account of what had stood there before them.
M41 and M42 status
Historic site of the Ullanor Crusade and Triumph.
Canonically the same world as Armageddon — teleported and re-colonised long ago.
Timeline
The Great Crusade breaks the Ork empire of Ullanor; the Ullanor Triumph crowns the victory and raises Horus to Warmaster.
The War of the Beast: a second Ork empire rises on Ullanor and is destroyed after bitter fighting.
The Mechanicus teleport the stripped world to the edge of Segmentum Solar and record it destroyed; it is later re-colonised as Armageddon.
Eastern campaign planners still cite the old Ullanor position as a symbolic military reference.
The archive keeps Ullanor marked as history — a triumph whose world now answers to another name.
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Cartographic positions and several administrative details are intentionally approximate where published Warhammer sources conflict or provide no canonical coordinate system.